1. Field of the Invention
The present invention is directed to an X-ray tube of the type having a cathode and an anode arranged in a vacuum housing, the electron beam emanating from the cathode being incident in a focal spot on the anode at which X-rays are produced, with means for deflecting the electron beam being provided.
2. Description of the Prior Art
The possibility of deflecting the electron beam, and thus the focal spot, is of significance, particularly in conjunction with computed tomography, since an improvement in the image quality can be achieved by the known measure of displacing the focal spot between two limit positions, thereby doubling the data available for the calculation of the image of a body slice.
European Application 0 460 421 discloses an X-ray tube of the type initially described, wherein the means for deflecting the electron beam are formed by a curved deflection coil surrounding a hollow cylindrical housing part, which connects the portion of the housing in which the cathode is disposed to the portion of the housing in which the anode is disposed. A problem arises given this X-ray tube that the deflection coil effects not only a deflection but also a defocusing of the electron beam. As a consequence of activation of the deflection coil, thus, the focal spot which arises on the incident surface of the anode at the point struck by the electron beam exhibits not only a displacement on the incident surface but also an undesired change in size and/or shape.